A 25 to 50 percent elevation in the glomerular filtration rate (GFR) is seen early in the course in up to one-half of patients with type 1 diabetes mellitus [1], an abnormality that is exaggerated after ingestion of a protein load [2]. Glomerular hypertrophy and increased renal size typically accompany the rise in GFR [2].

Hyperfiltration also occurs early in the course of type 2 diabetes [3,4]. In an original report of 110 newly diagnosed patients with type 2 diabetes mellitus, for example, the GFR was above 140 mL/min in 16 percent and more than two standard deviations above the mean of a control population in 45 percent [3]. The prevalence of hyperfiltration may be lower in the era of more aggressive glucose control. A later study of 93 newly diagnosed patients, for example, found that 17 percent had a GFR that was more than two standard deviations above the mean of a control population [5].

The degree of hyperfiltration and the course of the GFR in type 2 diabetes mellitus was evaluated in more detail in a study of 194 Pima Indians who had GFR measured using iothalamate clearance [4]. The following results were noted:

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